The tranistion altitude is not always 3000ft although is most commonly used. So if we take 3000 ft as the tranistion altitude then FL30 is the lowest possible FL.
OK....FL are based on 1013mb.
A heading of 075 is an odd heading so levels that we can fly are FL30, FL50, FL70 etc.
Now lets take your QNH of 1010mb Thisis 3mb lower than the 1013mb. lets remember that 1mb=30ft (actualy 27ft to be accurate). So 3mb multiplied by 30ft = 90ft.
3000ft - 90ft = 2010ft Therefore FL30 is not available so you would need to fly the next available FL for you altitude whcih is FL50.
Does that help?